1. Field of the Invention
The present invention generally relates to a method and an apparatus for converting analog images into digital images, and more particularly, to a method and an apparatus with auto-correcting phase for converting analog images into digital images.
2. Description of Related Art
Along with the progress in science and technology in recent years, a digital video system has gradually replaced a traditional analog video system. Accordingly, various digital audio/video products are more and more popular in our daily life, for example, audio/video disk, digital TV broadcast, image phone and video meeting.
To adapt the above-mentioned tendency with digital display, a digital video system often requires a digital image converting apparatus for converting an original analog display frame into a digital display frame. A common digital image converting apparatus includes an analog-to-digital converter (ADC) and a delay locked loop (DDL), wherein the DDL is for producing a clock signal and the ADC converts an analog display frame into a digital display frame according to the clock signal. Note that when the phase of the clock signal does not match the analog display frame, the digital video system would produce a blur frame.
In order to provide a solution targeting the above-mentioned problem, several conventional technologies are available currently, which are competent for correcting phases during converting an analog display frame into a digital display frame. The common conventional techniques are briefly depicted as follows.
The first one of the prior art utilizes a specific integrated circuit (specific IC) for locating the most appropriate edge within an analog display frame, wherein the so-called edge is an area having most-varied graylevels of pixels within the analog display frame. In addition, the first conventional technique further employs a DDL to adjust the phases of the clock signal produced by a phase locked loop (PLL), and the internal setting parameters of the DDL are controlled by a microprocessor. Whenever the DDL fine-adjusts the phase of the clock signal, the ADC would convert the analog display frame one time, and the microprocessor would record the value corresponding to the edge of the analog display frame into a registering block according to the converted frame. In this way, the microprocessor can locate a region in the registering block having the minimal continuous variation between a recorded value and the adjacent recorded value, wherein all values corresponding to the analog display frame are written in the registering block. Moreover, the microprocessor takes the phase corresponding to the middle position of the region as the optimal phase.
Note that during dynamically displaying frames, the edge of the analog display frame is varied with a motion of the images, which results in misjudging the optimal phase. In addition, to determine the most appropriate edge within an analog display frame, the first prior art must employ a specific IC having sophisticated circuit architecture to locate the appropriate edge within a display frame. In other words, the first prior art is suitable to search the optimal phase on a still analog display frame, not suitable for dynamic frames. In fact, the first prior art further is disadvantageous in a high system cost and requiring a sophisticated hardware architecture.
The second prior art is evolved from the first one, except that the second prior art uses an application software or a firmware initialization program to produce a specific analog display frame, where the edge on the specific analog display frame is given, so that the second prior art does not need a specific IC to search out the edge of a display frame.
However, during searching the optimal phase, a video system only displays the specific analog display frame and meanwhile the real frames must be quit for outputting. That is to say, the second prior art would produce a frame conflict issue, which degrades the display effect. In addition, a video system adopting the second prior art during a mass production needs to install an application software or a firmware initialization program for producing the specific analog display frame, which further affects the mass production yield.